1. Technical Field
The present invention relates generally to internal combustion engines and, more particularly, to a misfire detection apparatus and method for detecting misfire of individual cylinders in an internal combustion engine.
2. Discussion
The Clean Air Act (1955) required motor vehicle manufacturers to reduce exhaust emissions of carbon monoxide, hydrocarbons, and oxides of nitrogen from light duty motor vehicles. To comply with the Act, most motor vehicle manufacturers generally use catalytic converters on production vehicles to control such exhaust emissions. A catalytic converter typically includes a catalyst and operates at a very high temperature in order to burn unwanted byproducts of combustion so as to reduce hydrocarbons, carbon monoxide and nitrous oxide. However, increased amounts of unburned byproducts that often remain after the occurrence of an engine misfire can lead to damage of the catalytic converter.
More recently, regulatory agencies have proposed that passenger, light-duty and medium-duty motor vehicles with feedback fuel control systems be equipped with a malfunction indicator function that will inform the motor vehicle operator of any malfunction of an emission-related component that interfaces with an on-board computer of the motor vehicle. It is also proposed or required that an on-board diagnostic system identify the likely area of malfunction. Proposals or requirements have set forth catalyst, misfire, evaporative purge system, secondary air system, air conditioning system refrigerant, fuel system, oxygen sensor, exhaust gas recirculation, and comprehensive component monitoring requirements.
As previously mentioned, misfire of internal combustion engines can cause damage to the catalyst of a catalytic converter. With respect to misfire, the identification of the specific cylinder experiencing misfire may be required. Some regulations provide that the motor vehicle manufacturer specify a percentage of misfires out of the total number of firing events necessary for determining malfunction for: (1) the percent misfire evaluated in a fixed number of revolution increments for each engine speed and load condition which would result in catalyst damage; (2) the percent misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail a Federal Test Procedure (FTP) by more than 150% of the applicable standard if the degree of misfire were present from the beginning of the test; and (3) the degree of misfire evaluated in a certain number of revolution increments which would cause a durability demonstration motor vehicle to fail an inspection and maintenance (IM) program tailpipe exhaust emission test.
Current and proposed future regulations are also requiring that motor vehicle manufacturers be able to provide information detailing the occurrence of misfires such as identifying which cylinders are responsible for one or more misfires. The misfire information need be collected and stored in memory so that the stored information may be downloaded at a service center and used to determine the cause of misfires in the vehicle. One misfire detection and identification approach is disclosed in issued U.S. Pat. No. 5,361,629 issued Nov. 8, 1994 and titled "Single Sensor Misfire Detection Apparatus and Method for an Internal Combustion Engine". The above-cited patent is also hereby incorporated by reference. The misfire detection approach in the above-cited patent senses rotation of a crankshaft and calculates a crankshaft velocity based on the sensed rotation. The calculated crankshaft velocity changes or a compensated velocity change is compared to a predetermined crankshaft velocity range to determine if misfire occurred.
The above misfire detection approach compares crankshaft velocity change which does not compensate for normal engine acceleration. Furthermore, while a number of conventional approaches are capable of detecting a single misfire for a single cylinder, with misfires on cylinders which share a common coil and have a power stroke separated by 360.degree. may go undetected. Opposed cylinder fire detection is especially desirable for a distributorless ignition system (DIS) where cylinders are commonly paired on the same coil. For instance, in a DIS with a four-cylinder engine, the firing interval may follow the order of cylinders 1 3 4 2, where cylinders 1 and 4 share the same coil and cylinders 2 and 3 share another coil. The commonly shared cylinders are separated by 360.degree. of crankshaft rotation. If one of cylinders 1 or 4 is disconnected, a common mode failure may occur. This occurrence may result when a spark plug wire is disconnected for cylinder 1, which thereby results in dual cylinder misfires for cylinders 1 and 4. Detection of misfires for both cylinders is desired to help determine the cause of the misfire event.
It is therefore one object of the present invention to provide for an improved apparatus and method of detecting cylinder misfires in an internal combustion engine.
It is another object of the present invention to provide for a misfire detection apparatus and method which is capable of detecting opposed cylinder misfires for an internal combustion engine and which is capable of identifying which cylinders are responsible for the misfires.
It is yet another object of the present invention to provide for a misfire detection apparatus and method which compensates for normal engine accelerations, realizes a good signal to noise ratio and is capable of detecting multiple cylinder misfire events.